1. Field of the Invention
The present application relates to a method for growing silicon crystal, and more particularly to a method for growing monocrystalline silicon.
2. Description of the Related Art
In Czochralski method (CZ method) for growing monocrystalline silicon, oxygen may enter monocrystalline silicon because of the melt of quartz crucible. The oxygen mainly exists in silicon lattice space and precipitates when the concentration exceeds beyond its solubility in silicon, the oxygen precipitation defect is formed thereby. The oxygen precipitation defect may damage the integrated circuit device.
Intrinsic gettering technology means that a clean zone with a certain depth having no defects can be formed on the surface of silicon wafer by generating high density oxygen precipitation within the silicon wafer. The clean zone can be used for device manufacture. However, smaller character size is requested with development of ultra-large-scale integrated circuit (VLSI), so that the oxygen concentration in the monocrystalline silicon has to be reduced to prevent defect formation in the source area. Recently, since thermal budget of integrated circuit manufacture process is significantly reduced, it cannot provide suitable conditions for oxygen precipitation within the silicon wafer and the intrinsic gettering effect is adversely affected.
The above problems can be solved by nitrogen doping during growth of monocrystalline silicon in Czochralski method. Nitrogen is able to facilitate oxygen precipitation within monocrystalline silicon; therefore the intrinsic gettering effect can be enhanced. Further, nitrogen doping is able to increase mechanical strength of the silicon wafer and reduce void defect. Distribution of oxygen precipitation is studied by infrared light scattering tomography (IR-LST) and scanning infrared microscopy (SIRM). It shows that, after one-step thermal annealing of a nitrogen doped 300 mm silicon wafer with suitable nitrogen doping concentration, a high density oxygen precipitation can be generated and a clean zone with a certain depth can be formed near the surface of the wafer. Further, with the increasing nitrogen concentration, the radial distribution of oxygen precipitation becomes more homogeneous.
In this industry, it is general to apply solid-phase nitrogen doping, e.g. powder of silicon nitride (Si3N4), to dope nitrogen into monocrystalline silicon. The solid-phase nitrogen doping is able to control the nitrogen concentration, but it is difficult to obtain Si3N4 powder with high purity. Si3N4 particle often remains because of its difficult melting property. Therefore, dislocation free monocrystalline silicon cannot be formed. Gas-phase nitrogen doping is also applied in this industry, in which high purity nitrogen gas or nitrogen/argon mixture gas is introduced after seeding. The nitrogen doping concentration in the silicon crystal is controlled by the time period of nitrogen introduction. The gas-phase nitrogen doping is achieved by the reaction of the nitrogen gas and the silicon melt, so that the purity is relative high and the silicon nitride particle is not easily formed. However, it is difficult to control the process and the nitrogen concentration since the reaction of gas-phase nitrogen doping is totally based on thermal convection.
According to the above, a method for manufacturing monocrystalline silicon is still required.